In chemical experiments, during the process of the external operations, often biochemical substances that are harmful to humans are produced. Fume hoods are used as one type of equipment to prevent these biochemical substances from being diffused into a room and to prevent them from coming into contact with the human body. Typically, fume hoods are provided with an enclosure with a sash that can be opened either vertically or horizontally, where an operator in the laboratory can access the inside of the enclosure through the sash. So that the operator will not be exposed to harmful biochemical substances during the operations using the fume hood, the enclosure is connected to a local exhaust duct that removes the biochemical substances.
The flow rate controlling system is a system for regulating the rate of flow in a local exhaust duct so as to maintain the planar air flow rate within a sash plane at a prescribed speed so that no biochemical substance returns back into the room when an experiment involving a biochemical substance is performed within a flow hood, and to maintain a constant room pressure so that the biochemical substance will not leak out from the room and so that contaminants, and the like, from the outside it will not flow into the room. See, for example, Japanese Unexamined Patent Application Publication No. 2012-237527 (the “JP '527”). FIG. 4 is a diagram illustrating a structure for a conventional flow rate controlling system. The flow rate controlling system comprises: fume hoods 101-1 and 101-2 that are disposed within the room 100; local exhaust ducts 102-1 and 102-2 that are connected to the fume hoods 101-1 and 101-2; a supply air duct 103 for supplying supply air to the room 100; a common exhaust duct 104 for the air of the room 100; local exhaust air valves EXV1 and EXV2 for regulating the airflow rates of the local exhaust ducts 102-1 and 102-2; a supply air valve MAV for regulating the airflow rate of the supply air duct 103; a common exhaust air valve GEX for regulating the airflow rate of the common exhaust duct 104; controllers 105-1 and 105-2 for controlling the local exhaust air valves EXV1 and EXV2; a controller 106 for controlling the supply air valve MAV; a controller 107 for controlling the common exhaust air valve GEX; and communication lines 108 for connecting together the various controllers 105-1, 105-2, 106, and 107.
The fume hoods 101-1 and 101-2 are provided with sashes 111-1 and 111-2; personnel-detecting sensors 112-1 and 112-2 for detecting whether or not there is a person within the range of detection; fume hood monitors 113-1 and 113-2 for providing information to operators using the fume hoods 101-1 and 101-2; and sash sensors 114-1 and 114-2 for detecting the degrees to which the sashes 111-1 and 111-2 are open.
In the flow rate controlling system illustrated in FIG. 4, control of the openings of the supply air valve MAV, the common exhaust air valve GEX, and the local exhaust air valves EXV1 and EXV2 is carried out so that the supply air flow rate of the supply air duct 103, the exhaust flow rate of the common exhaust duct 104, and the local exhaust flow rates of the local exhaust ducts 102-1 and 102-2 will satisfy the relationship that “the supply air flow rate=the common exhaust flow rate+the local exhaust flow rates+an offset flow rate,” that is, the flow rate balance control is performed.
In the flow rate controlling system illustrated in FIG. 4, if there is a master valve that oversees the flow rate balance control (for example, the supply air valve MAV) and a follower valve (for example, the common exhaust air valve GEX) that operates after having received the flow rate set point from the master valve, the master valve changes the flow rate for both the master valve and the follower valve without being able to detect a fault in the follower valve, and thus there is a problem in that in some cases the balance of the flow rates within the room may be disrupted (that is, only the master valve is opened or shut, regardless of a fault in a follower valve that prevents it from opening or shutting).
For example, let us assume that in a room that is maintained at a negative pressure, the supply air flow rate and the exhaust flow rate when operating at night, where the air turnover rate is reduced, is at a supply air flow rate of 1500 m3/hour with a common exhaust flow rate at 2000 m3/hour (with the local exhaust flow rates at 0 m3/hour).
If there is a fault in the common exhaust air valve that prevents the flow rate from being increased or decreased then, when there is an operation that attempts to increase the turnover rate of the air during the daytime, the supply air flow rate may be set to 3000 m3/hour with the common exhaust flow rate at 2000 m3/hour, so the exhaust flow rate will be insufficient when compared to the normal common exhaust flow rate of 3500 m3/hour, causing the interior of the room to go to an extremely positive pressure.
The present invention was created in order to solve the problem set forth above, to provide a flow rate controlling system and flow rate controlling method wherein the room pressure will not go to an extremely positive pressure or an extremely negative pressure even if there is a fault in the supply or exhaust air valve.